Often, fasteners used to assemble performance critical components are tightened to a specified torque level to introduce a “pretension” in the fastener without damaging the substrate in which the fastener is positioned. As torque is applied to the head of the fastener, beyond a certain level of torque the fastener begins to stretch. This stretch results in the pretension in the fastener which then holds the components together. A popular method of tightening these fasteners is to use a torque wrench. Accurate and reliable torque wrenches help insure the fasteners are tightened to the proper torque specifications.
Torque wrenches vary from simple mechanical types to sophisticated electronic types. Mechanical type torque wrenches are generally less expensive than electronic ones. There are two common types of mechanical torque wrenches, beam and clicker types. With a beam type torque wrench, a beam bends relative to a non-deflecting beam in response to the torque being applied with the wrench. The amount of deflection of the bending beam relative to the non-deflecting beam indicates the amount of torque applied to the fastener. Clicker type torque wrenches work by preloading a snap mechanism with a spring to release at a specified torque, thereby generating a click noise. Other types of mechanical torque wrenches include indicating, ratcheting, torque limiting, in-line and beam styles of torque wrenches. In an indicating wrench, torque value is measured and displayed on a scale. In a torque limiting wrench, the wrench will drive the fastener until a preset torque value is reached at which point the wrench will slip and cease to transmit the torque applied. In a ratcheting mechanism wrench, in order to drive a fastener into a substrate such as wood or bone it is necessary to rotate the fastener through multiple rotations about its axis. For a hand held tool, in order to drive fasteners, typically the user will have to change their grip or change hands in order to keep driving the fastener due to the limitation of the range of motion of the bones joint in a human hand, which occurs at approximately 100 to 180 degrees depending on the person. A ratcheting mechanism in a fastener driver tool allows the user to rotate the instrument in the opposite direction to the torque being applied without lifting or otherwise disengaging the device driving bit from the fastener and without lifting the hand off the device or changing hands. With a ratcheting mechanism in the tool the user can rotate the tool and drive the fastener through as many degrees of rotation as their hand allows and then ratchet the driving tool in the opposite direction so as to be able to drive the fastener through as many degrees without lifting the hand off the driving tool.
Electronic torque wrenches (ETWs) tend to be more expensive than mechanical torque wrenches, and more accurate as well. When applying torque to a fastener with an electronic torque wrench, the torque readings indicated on the display device of the electronic torque wrench in a visible manner, such as by a numeric or light indication, and are proportional to the pretension in the fastener due to the applied torque. However, the readings also depend on, among other factors, the under head friction between the head of the fastener and the adjacent surface of the component and the friction between the mating threads. Static friction is greater than dynamic friction. Therefore, when torquing operations are initiated, increased amounts of torque may be required to overcome static friction forces and initiate rotation of the fastener. Therefore, it follows that torque is preferably applied to the fastener in a slow and continuous manner to allow friction forces to stabilize, to help insure accuracy and to help prevent over-torquing, which can result in damage being done to the fastener or the substrate, with extreme cases resulting in destruction of the fastener or substrate. As well, it is often desirable for the user to see both the current torque value (torque being applied at that instant) and the peak torque value (maximum torque applied up to the present instant) simultaneously. However, existing torque wrenches typically display only the current torque value or the peak torque value at any given time.
When a torque wrench is operated in a “tracking mode,” the current torque value is displayed and the user therefore does not necessarily get immediate feedback regarding the actual peak torque value to which the fastener may have been subjected. Although with some electronic torque wrenches it is possible to get this information by downloading the data, this action is typically not instantaneous and, therefore, the operator does not get immediate feedback. On the other hand, when operating in a “peak hold mode,” the display of the electronic torque wrench typically shows only the maximum torque applied to the fastener up to that time. In the peak hold mode, the user is often ignorant of the current torque level, which can lead to either over or under-torquing the fastener.
Another factor that can affect the accuracy of a reading on an electronic torque wrench is the operating temperature. Strain gages that are used in electronic torque wrenches to measure applied torque are often affected by temperature. Therefore, to obtain accurate torque measurements, it is often necessary to measure the existing temperature and adjust the displayed torque value for a given strain gauge reading.
Regardless of which type ETW is used, torque extensions may be required to tighten fasteners that are in locations that the torque wrench will not reach. One of the most common methods of attaching a torque extension to an ETW is to replace the original drive head with an extension that has its own drive head. Once the extension is inserted, the readings of the ETW must usually be corrected for any change in lever arm length due to the extension. With the extension in place, the actual torque experienced by the fastener will be either higher or lower than what is actually displayed on the ETW, depending on whether the extension extends outwardly or inwardly from the end of the ETW, respectively.
As a result of these and other issues with prior art electronic torque wrenches, it is desirable to develop an electronic torque wrench that addresses these limitations as well as having other user-friendly features to increase the utility of the wrench.